This invention relates generally to solar collector systems and more particularly to controls for such systems.
Solar collector systems differ in complexity, but almost all require some type of control. It is desirable for example to start circulation of the liquid to be heated when the insolation is adequate. In a system employing a water/ethylene glycol mixture as the heat transfer liquid, provision must also be made to prevent over heating of the liquid which will cause it to break down. Such over heating can occur in two ways; first, if an insufficient amount of the energy collected is being utilized, the temperature of the liquid will rise; and second, if the pump circulating the liquid should stop, for example because of loss of electric power, the liquid in the collector will become over heated.
An additional problem is excessive starting and stopping of the circulating pump. This can happen if a temperature sensor indicates the collector is hot, so the pump starts; but the cool liquid flowing through it cools it down enough so that the temperature sensor indicates the collector is cool and the pump stops.
Consequently, the system and its controls should incorporate features which avoid these problems.